The present invention relates generally to high-pressure fuel injection valves or injectors for internal combustion engines, and, more specifically, to an injection valve that is directly controllable by a position actuating magnetostrictive material and that includes a passive hydraulic link.
Direct injection of a gaseous fuel into the combustion chamber of an internal combustion engine is desirable for several reasons. For example, direct injection allows charge stratification, eliminating throttling losses associated with homogeneous charge engines. Additionally, with direct injection late in the compression stroke, a high-compression ratio can be maintained, maintaining the efficiency of conventional diesel engines. Further, when the fuel that is directly injected comprises natural gas, propane, or hydrogen, the emissions of NOx and particulate matter (PM) are significantly reduced. The directly injected gaseous fuel can be ignited with a glow plug, with a spark plug, with pilot diesel fuel, or with any other energy source. The gaseous fuel needs to be injected at high pressure to overcome the combustion chamber pressure, which is high at the end of the compression stroke. Preferably, the injection pressure is high enough to promote good mixing between the injected fuel and the combustion chamber air.
Direct injection at high pressures presents several challenges. The use of high pressure fuels for direct injection results in high fuel pressures existing within the injection valve or injector. As a result, when closed, the injection valve should typically be strongly seated to avoid leakage of the fuel into the combustion chamber between injection events. When the valve is a needle valve, the valve is seated when the sealing surfaces of the movable valve needle and the valve seat are in fluid-tight contact with each other. The valve seat is generally part of the valve housing or body.
Moreover, compared to low-pressure systems, higher forces are needed to open the injection valve since the valve should be strongly seated to remain sealed when the valve tip is exposed to the high pressures generated in the combustion chamber. High closing forces are also involved since the needle of a fuel injection valve for a high-pressure system should overcome the high forces generated by the exiting pressurized fuel when the needle is in the open position.
Additionally, there is only a small window of time during which the fuel can be injected. For example, at 4500 revolutions per minute (RPM), at full load, all of the fuel is preferably injected in less than 2-3 milliseconds.
Nearly all known direct fuel injection systems in internal combustion engines have been hydraulically-actuated. These systems rely on a hydraulic fluid to provide the force to open a fuel injection valve (or valves, when the engine comprises a plurality of combustion chambers). Accordingly, at typical engine operating speeds, hydraulically actuated fuel injection valves rely on rapid changes in the hydraulic fluid pressure to open and close the injection valve(s). An injection valve is typically opened by increasing the hydraulic fluid pressure and closed by reducing the hydraulic fluid pressure, such that the opening force applied to the injection valve is reduced, causing the valve to close. However, in the context of a gaseous fuel injection valve, hydraulic operation presents several drawbacks, including:
the need for additional hydraulic hardware such as a hydraulic pump, valves, and a reservoir for the hydraulic fluid;
the need for a seal to be established between the variable pressure hydraulic fluid and the high pressure gaseous fuel;
increased bulkiness of the injection valve assembly because of the additional hardware requirements; and
delayed response of the system caused by time delays of the hydraulic fluid between the electrical valve hardware and the needle that controls gas flow from the injector.
Moreover, the degree of controllability of the movement of the injection valve is low when the motive force is provided by a pressurized fluid rather than by a directly controllable source. In this respect, it is difficult to control lift, resulting in limited lift control capabilities when using a double-spring configuration. Therefore, it is desirable to avoid the use of hydraulics to operate gaseous fuel injectors, particularly for high-speed engines. xe2x80x9cLiftxe2x80x9d in the context of injection valves is defined herein as the displacement of the valve needle away from its closed/seated position to its open position.
An injection valve injects fuel into a combustion chamber of an internal combustion engine. The injection valve comprises:
(a) a valve housing comprising:
a fuel inlet port;
an interior chamber fluidly connected to the fuel inlet port;
a nozzle comprising at least one nozzle orifice providing a fluid passage from the interior chamber to the combustion chamber;
(b) a valve needle formed from a ferromagnetic material and disposed within the valve housing wherein the valve needle is movable between a closed position at which a sealing end of the valve needle contacts a valve seat to fluidly seal the interior chamber from the nozzle orifice, and an open position at which the sealing end of the valve needle is spaced apart from the valve seat whereby the interior chamber is fluidly connected with the nozzle orifice;
(c) a needle biasing mechanism associated with the valve needle, the needle biasing mechanism applying a closing force to the valve needle for biasing the valve needle in the closed position; and
(d) an actuator assembly associated with the valve needle and disposed in the interior chamber, the actuator assembly comprising a magnetostrictive member actuatable to expand in length and apply an opening force to the valve needle stronger than the closing force, thereby moving the valve needle to the open position.
In a preferred injection valve, the actuator assembly is disposed within the interior chamber in an annular space surrounding at least a portion of the valve needle. The preferred needle biasing mechanism is a spring, most preferably at least one disc spring.
Locating the actuator assembly in an annular space that surrounds a portion of the valve needle is a preferred arrangement because it allows for a compact design. The actuator assembly is typically elongated and has a length that is determined by the desired lift, which in turn determines the length of the magnetostrictive member. When a magnetostrictive actuator is actuated, a magnetic field is applied to the magnetostrictive member to cause it to expand in length. Longer magnetostrictive members are able to expand by greater amounts, resulting in greater lift when used in an injection valve application.
Conventional devices with similar arrangements (that is, a solid member extending through a tubular magnetostrictive member) employ a non-ferromagnetic member to avoid interfering with the magnetic field. In the field of magnetostrictive materials, it is generally believed that employing a ferromagnetic material for the valve needle will cause leakage of magnetic flux, which may in turn compromise performance since all flux is intended to pass through the tubular magnetostrictive member and the flux paths provided by conventional poles and flux tubes. Consistent with such beliefs, conventional devices with similar arrangements have employed non-ferromagnetic materials such as, for example, austenitic stainless steel, titanium and ceramics.
Compared to ferromagnetic materials, there are a number of disadvantages of employing such non-ferromagnetic materials. For example, titanium and ceramics are generally more expensive and more difficult to machine to high tolerances, compared to ferromagnetic materials such as tool steel. In addition, non-ferromagnetic materials such as titanium and austenitic stainless steel generally can not be hardened to match the durability of ferromagnetic materials. Past approaches to solving some of these disadvantages have included coating the non-ferromagnetic material to improve its durability. Another approach is to use multi-part components comprising, for example, a non-ferromagnetic member extending through the sections where a magnetic field is generated and a ferromagnetic material such as tool steel for the needle tip which impacts against the valve seat.
Although the phenomena of the present injection valve with a ferromagnetic needle is not fully understood, it has been found that, contrary to general beliefs in the field of magnetostrictive materials, a ferromagnetic material can be employed for a valve needle that extends through a tubular magnetostrictive member. It is hypothesized that due to the high frequency switching of the magnetic field during the injection period, the eddy current skin depth of the needle shields the needle from the magnetic circuit and thereby prevents the needle from draining flux from the circuit.
The ferromagnetic material for the valve needle is preferably a suitable tool steel. For example, a tool steel such as H type or M type is a preferred material for the valve needle.
The injection valve preferably further comprises a hydraulic link assembly comprising a passive hydraulic link having a hydraulic fluid thickness through which the opening and closing forces are transmitted. The hydraulic fluid acts substantially as a solid with the thickness being substantially constant while the actuator assembly is activated and wherein the thickness of the hydraulic link is adjustable while the actuator is not activated in response to changes in the dimensional relationship between components of the injection valve to maintain a desired valve lift upon activation of the actuator assembly.
In a preferred embodiment, the thickness of the hydraulic link is auto-adjustable in response to changes in the dimensional relationship caused by differential thermal expansion, variations in manufactured dimensions within design tolerances, and/or wear to components of the injection valve. The hydraulic link assembly preferably comprises a sealed hydraulic cylinder, with a piston and hydraulic fluid disposed within the hydraulic cylinder. The piston may be an integral part of the valve needle.
The actuator assembly preferably comprises an electric coil disposed around the magnetostrictive member and a flux tube disposed around the electric coil. In preferred arrangements, the actuator assembly may be disposed within the interior chamber of the injection valve. In a particular preferred embodiment, the actuator assembly is tubular and disposed within an annular space around a cylindrical portion of the valve needle. One end of the tubular actuator assembly may be held in a fixed position in relation to the valve housing by a pole that supports the magnetostrictive member. The pole is attached to the valve housing to prevent movement of the supported end of the magnetostrictive member when the actuator assembly is activated. In one embodiment, the flux tube and/or the pole associated with the valve housing are integral parts of the valve housing and/or the magnetostrictive member. In this arrangement, the valve housing advantageously also acts as the flux tube and obviates the need for a separate component.
In a preferred embodiment, the injection valve comprises an inlet port and nozzle orifices arranged substantially at opposite ends of the injection valve. Fluid passages are provided through or between the actuator and hydraulic link assemblies and the valve housing to allow fuel to flow from the inlet port to the nozzle orifices. The flow of fuel through such fluid passages helps to cool the actuator and hydraulic link assemblies. Such fluid passages may be formed by providing longitudinally-oriented grooves in the surfaces of components of the actuator assembly and the hydraulic cylinder and/or longitudinally-oriented grooves in the inner wall of the valve housing. Providing port openings through components of the actuator, the hydraulic link assemblies, and the valve housing may also form such fluid passages.
The actuator assembly is controllable to control the desired lift between 10 and 100 percent of maximum lift. That is, the control pulse directed to the actuator assembly can be modulated to provide full or partial lift, as desired. The control pulse is a modulated electric current directed to an electric coil that produces a magnetic field.
The present injection valve is particularly suited for injecting a gaseous fuel because the ability to modulate the movement of the valve needle may be beneficially used to slow down the closing action of the valve needle to reduce impact upon closing. When a liquid fuel is injected, the closing impact is dampened by the displacement of the thin liquid fuel layer, which is considerably denser than gaseous fuels. When the fuel is a gaseous fuel, it can be injected into the combustion chamber at a pressure greater than about 2000 psi (about 13.8 MPa).
A magnetostrictive material that is suitable for use in the present injection valve comprises a material known as ETREMA Terfenol-D(copyright) magnetostrictive alloy that is available from Etrema Products Inc. ETREMA Terfenol-D(copyright) magnetostrictive alloy is a metal alloy composed of the elements terbium, dysprosium, and iron.
In a preferred embodiment, the valve needle, actuated by a magnetostrictive assembly is controllable to move between the closed and open positions in less than about 250 microseconds.
To improve the range of valve lift for an actuator comprising a magnetostrictive member with a given length, a compressive force may be applied to the magnetostrictive member. The net displacement may be increased per respective unit of applied magnetic field by pre-loading the magnetostrictive member. Accordingly, a compression spring member may be employed for applying a compressive force to pre-load the magnetostrictive member. In a preferred embodiment, the compression spring member comprises at least one disc spring (also known as a Belleville spring or Belleville washer).
The injection valve housing may comprise a plurality of parts that are joined with each other to provide a fluidly sealed body. For example, the valve housing may comprise a hollow main housing with a removable valve cap that allows access to the valve components disposed within the main housing. The valve housing may further comprise a separate valve tip so that it is replaceable when worn. In addition, the valve tip may be designed so that it is the only portion of the valve body that is directly exposed to the interior of the combustion chamber. In this case the valve tip may be formed from a material that will provide greater durability when directly exposed to the conditions that might be expected within a combustion chamber.
While the hydraulic link is designed to compensate for changes in the dimensional relationships between valve components, including changes caused by differential thermal expansion, the demands placed upon the hydraulic link may be reduced by the selection of materials for the valve components that have similar thermal expansion coefficients.
A preferred fuel injection valve for an internal combustion engine comprises:
(a) a valve housing comprising:
a fuel inlet port;
an interior chamber fluidly connected to the fuel inlet port;
a nozzle comprising a valve seat and a nozzle orifice providing a fluid passage from the interior chamber to the combustion chamber;
(b) a valve needle formed from a ferromagnetic material comprising a cylindrical portion having a sealing end and a piston portion having a pre-load end, the valve needle disposed within the valve housing wherein the valve needle is movable between a closed position at which the sealing end contacts the valve seat to fluidly seal the interior chamber from the nozzle orifice, and an open position at which the sealing end is spaced apart from the valve seat whereby the interior chamber is fluidly connected with the nozzle orifice, wherein valve lift equals distance traveled by the sealing end away from the valve seat;
(c) a needle spring associated with the pre-load end of the valve needle, wherein the needle spring is compressed to apply a closing force to the valve needle for biasing the valve needle in the closed position;
(d) an actuator assembly that may be activated to apply an opening force to the valve needle that is stronger than the closing force, for moving the valve needle to the open position, the actuator assembly comprising:
a tubular magnetostrictive member disposed around the cylindrical portion of the valve needle;
an electrical coil disposed around the magnetostrictive member;
a flux tube disposed around the electrical coil; and
a support for the actuator assembly that acts as a pole and provides a fixed position for one end of the magnetostrictive member relative to the valve housing; and
(e) a hydraulic link assembly comprising a sealed hydraulic cylinder disposed about the piston portion of the valve needle, a hydraulic fluid disposed within the hydraulic cylinder, wherein the opening and closing forces applied to the valve needle are transmitted through a thickness of the hydraulic fluid whereby the hydraulic fluid acts as a hydraulic link and the thickness is automatically adjustable in response to changes in the dimensional relationship between components of the injection valve to maintain a desired valve lift when the actuator assembly is activated.
These and other advantages are provided by a directly actuated injector as described below.